ATC350SX Build Thread - Shaft drive 350x concept

[ps2fixer]

I haven't found a quad in my area for under $1000 in years. I'll be about $500 into this project if I bought the 200x front end off the guy local to me. Getting the front end geometry right isn't my strongest area, so I'd rather start with a machine that already has that figured out. I'd love to throw a bigger engine in, but I know next to nothing about them, and some of the interchanges I have in mind won't work for those at all. Not sure if the TRX350D engine is any lighter, but trying to keep weight down even though it's shaft drive which is why I'll probably do a starter and battery delete. I could have always gone with a big bore kit on a 250sx engine but I've had this 350d for a while and my original plans for it has changed. I really love how the 350x engine runs, might just be because it's a bigger engine than the 250es/sx. The 450 foreman engine runs nothing like the 350x though, it runs much closer to the 250es/sx engine. Know pretty much nothing about the 420 and 500 machines but I suspect they run similar to the 450.

I think my area is a bit unique, we have a LOT of auto mechanics, there's so many people that the wadges they make is pretty low for the work involved (rust belt etc). There's a lot of people that work on their own machines at home here too. I find some of the most trashed rigged up machines around here even though it happens everywhere I'm sure.

I've been wanting to atleast try this project for a few years, just looking for a cheap 250sx parts machine hasn't worked out so I went after getting the bare min, frame and such.



This reminds me, here's an interchange I found no one even mentioning online. The trx350/350D shift "cage" does function in a 250es/sx machines. You can see in the pic the opening is wider so the shifter travels further for the shifts. There might be an issue down shifting if the shifter hits the foot peg, but it does fit in the engine in either case.

Also the shift shafts interchange, but shifter sticks out from the engine much further though. I'll probably have to put the 250sx shift shaft into the 350d engine to make it have a good shifter location.


350d left, 250sx right



350d top, 250sx bottom

[Homeless Dave]

I am curious to see how this project comes out. I think that the longer sifter shaft would make it easy to run a heel toe style shifter from a motorcycle, assuming there is not issues with the back part of the shifter hitting the fender.

[ps2fixer]

Well I screwed up the numbers, the older models included the output shaft gearing as part of the final gear ratio. All of the machines use the same gear set except the 250sx. With 25in tires and the 250sx diff I'll be around the 250sx stock gearing, 250sx diff + 5th gear swapped out to the trx300 one would be close to 250sx gearing with 22in tires and close to 350x gearing with 25in tires. I have to split the case, so I'll have to check out where to get the gears. Looks like the 250sx also has the same number of teeth for 5th gear as the trx300 but different part number. Being the 300 and 350 seem to be closer related engines, I suspect the 5th gear from the 300 might work in the 350, but the 250sx I have on hand already. The other interesting thing is the 350's 5th gear is the same teeth count as the 250es.

I'm digging in the service manual, and the measurements given seem to line up for the trx300, trx350, and 250sx transmissions for 5th gear atleast. It kind of sounds like this might be possible to swap the gears around.

[Tri-Z 250]

It’s gonna make a sick mudder, and understand the need to work with what you have.

[MrConcdid]

Ps2fixer;

You mentioned front end geometry not being your strong suit. If I were to do it, I would just weld up a fixture on my table. mount the 200x frame in a jig run a pipe through the neck and weld it to my table (braced of course)
mark and secure the neck and cut off the rest of the frame leaving the neck in place. put the atv frame on to the table establish height and squareness and weld the 200x neck in place to the atv frame. Your smart enough to figure out an even a better way if you wanted, that was just the first way that came to mind. angle finders are fine, I like to use them as a checking tool, not a building tool.


Cant wait to see this come together.
MrC.

[Rajunrick]

Here are the gear ratios for the 350D, the 350X, and the 250SX.

[ps2fixer]

Haha, have to love my site popping up in my own thread xD

Source is https://atvmanual.com =)

[Rajunrick]

Well, I thank you for that site. I've used it a couple of times now.

[ps2fixer]

Yea, not a problem, the site grew quite a lot since it launched. There's a lot of data on there, but I have soo soo soo much more to add. I'm delaying updating the site till I do a slight redesign to make google more happier, and make the management system more flexible. Like the 83-85 atc200x has all very similar specs, google doesn't like the 3 pages being almost exactly the same, so combining them into 1 page will make google happier.

[LA 3W]

Well I screwed up the numbers, the older models included the output shaft gearing as part of the final gear ratio. All of the machines use the same gear set except the 250sx. With 25in tires and the 250sx diff I'll be around the 250sx stock gearing, 250sx diff + 5th gear swapped out to the trx300 one would be close to 250sx gearing with 22in tires and close to 350x gearing with 25in tires. I have to split the case, so I'll have to check out where to get the gears. Looks like the 250sx also has the same number of teeth for 5th gear as the trx300 but different part number. Being the 300 and 350 seem to be closer related engines, I suspect the 5th gear from the 300 might work in the 350, but the 250sx I have on hand already. The other interesting thing is the 350's 5th gear is the same teeth count as the 250es.

I'm digging in the service manual, and the measurements given seem to line up for the trx300, trx350, and 250sx transmissions for 5th gear atleast. It kind of sounds like this might be possible to swap the gears around.

The 250 ES/SX engine is actually more of a sibling to the 300 than the 350D.

[ps2fixer]

Yea, the 350D has a pretty unique design vs the 250es/sx. The "easy" swap is the trx300 engine, but it's more of a utility engine than a sport engine. More cc still makes more power though.

[350for350]

Since this was brought back up, how's it coming along?

[ps2fixer]

I haven't sourced a front end yet for the build so it's been stalled for a while sadly. I've also been busy trying to expand my business, moved from atv harnesses/pigtails/adapters into automotive parts. Most recent research is a simplified harness for derby cars (the bare min wiring to make the vehicle run/move).

[350for350]

Someday. That's when a lot of my projects are going to be done too.

[ps2fixer]

Haha yea, it's not high on the list, it doesn't put food on the table or pay bills =). I'm sure I'll do it eventually, but everyone knows that means probably years xD.